Photoacid-generating copolymer and associated photoresist composition, coated substrate, and method of forming an electronic device

ABSTRACT

A copolymer include repeat units derived from an acid-labile monomer, an aliphatic lactone-containing monomer, a C 1-12  alkyl (meth)acrylate in which the C 1-12  alkyl group includes a specific base-soluble group, a photoacid-generating monomer that includes an aliphatic anion, and a neutral aromatic monomer having the formula 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2 , R 3 , X, m, and R 5  are defined herein. The copolymer is used as a component of a photoresist composition. A coated substrate including a layer of the photoresist composition, and a method of forming an electronic device using the coated substrate are described.

FIELD

The present invention relates to photoacid-generating copolymers usefulas components of photoresist compositions.

INTRODUCTION

Chemical compounds that decompose to generate acids when exposed toelectron beam or extreme ultraviolet radiation, also known as photoacidgenerators, are the basis for chemically amplified deprotection orcrosslinking of polymers in chemically amplified photoresistcompositions for microelectronics fabrication. The photoacid generatorsare incorporated into photoresist compositions as separate compounds, oras repeat units within copolymers. Existing photoresist compositionsprovide a useful balance of radiation sensitivity, resolution, and linewidth roughness. However, there is a desire for photoresists exhibitingincreased ultimate resolution, reduced mottling (top roughness), andincreased depth of focus without substantially compromising radiationsensitivity and/or line width roughness.

SUMMARY

One embodiment is a copolymer comprising repeat units derived from anacid-labile monomer; an aliphatic, lactone-containing monomer; abase-soluble monomer comprising a1,1,1,3,3,3-hexafluoro-2-hydroxyprop-2-yl substituent or a—NH—S(O)₂—R^(b) substituent wherein R^(b) is C₁₋₄ perfluoroalkyl; aphotoacid-generating monomer comprising an aliphatic anion; and aneutral aliphatic monomer having the formula

wherein R¹, R², and R³ are each independently hydrogen, halogen, C₁₋₆alkyl, or halogenated C₁₋₆ alkyl; m is 0 or 1; X is —O—, —C(O)—,—C(O)—O—, —S—, —S(O)—, —S(O)₂—, —S(O)₂—N(R⁴)—, —N(R⁴)—S(O)₂—, C₁₋₁₂hydrocarbylene, —O—(C₁₋₁₂ hydrocarbylene)-, —(C₁₋₁₂ hydrocarbylene)-O—,or —C(O)—O—(C₁₋₁₂ hydrocarbylene)-, wherein R⁴ is C₁₋₆ alkyl; and R⁵ isan unsubstituted or substituted C₁₋₂₄ alkyl.

Another embodiment is a photoresist composition comprising the any ofthe copolymers described herein.

Another embodiment is a coated substrate comprising: (a) a substratehaving one or more layers to be patterned on a surface thereof; and (b)a layer of the photoresist composition over the one or more layers to bepatterned.

Another embodiment is a method of forming an electronic device,comprising: (a) applying a layer of the photoresist composition on asubstrate; (b) pattern-wise exposing the photoresist composition layerto extreme ultraviolet or electron beam activating radiation; and (c)developing the exposed photoresist composition layer to provide a resistrelief image.

These and other embodiments are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows 24 nanometer contact hole performance for ComparativeExamples 1 and 2 (FIGS. 1( a) and (d), respectively), 22 nanometerline/space performance for the Comparative Example 1 (FIG. 1( b)), and17 nanometer line/space performance for Comparative Example 2 (FIG. 1(c)).

FIG. 2 is a plot of dissolution rate as a function of exposure dose forthe photoresist compositions of Comparative Examples 1 and 2.

FIG. 3 shows top-down scanning electron microscopy (SEM) images forComparative Example 3 at 26 nanometer critical dimension, andComparative Examples 6, and 7, and Examples 1 and 3 at 21 nanometercritical dimension after extreme ultraviolet (EUV) patterning.

FIG. 4, on the left side, shows 26 nanometer line/space performance forthe inventive photoresist composition of Example 2 and the comparativephotoresist composition of Comparative Example 8; on the right side arecorresponding plots of critical dimension versus focus as a function ofdose symbolized with different line types.

FIG. 5, on the left side, shows 22 nanometer line/space performance forExample 2 and Comparative Example 8; on the right side are correspondingplots of critical dimension versus focus as a function of dose.

DETAILED DESCRIPTION

The present inventors have determined that the copolymers describedherein provide photoresist compositions with increased ultimateresolution, reduced mottling (top roughness), and increased depth offocus without substantially compromising radiation sensitivity and/orline width roughness.

One embodiment is a copolymer comprising repeat units derived from anacid-labile monomer; an aliphatic, lactone-containing monomer; abase-soluble monomer comprising a1,1,1,3,3,3-hexafluoro-2-hydroxyprop-2-yl substituent or a—NH—S(O)₂—R^(b) substituent wherein R^(b) is C₁₋₄ perfluoroalkyl; aphotoacid-generating monomer comprising an aliphatic anion; and aneutral aliphatic monomer having the formula

wherein R¹, R², and R³ are each independently hydrogen, halogen, C₁₋₆alkyl, or halogenated C₁₋₆ alkyl; m is 0 or 1; X is —O—, —C(O)—,—C(O)—O—, —S—, —S(O)—, —S(O)₂—, —S(O)₂—N(R⁴)—, —N(R⁴)—S(O)₂—, C₁₋₁₂hydrocarbylene, —O—(C₁₋₁₂ hydrocarbylene)-, —(C₁₋₁₂ hydrocarbylene)-O—,or —C(O)—O—(C₁₋₁₂ hydrocarbylene)-, wherein R⁴ is C₁₋₆ alkyl; and R⁵ isan unsubstituted or substituted C₁₋₂₄ alkyl.

Except as otherwise specified, “substituted” shall be understood to meanincluding at least one substituent such as a halogen (i.e., F, Cl, Br,I), hydroxyl, amino, thiol, carboxyl, carboxylate, ester (includingacrylates, methacrylates, and lactones), amide, nitrile, sulfide,disulfide, nitro, C₁₋₁₈ alkyl, C₁₋₁₈ alkenyl (including norbornenyl),C₁₋₁₈ alkoxyl, C₂₋₁₈ alkenoxyl (including vinyl ether), C₆₋₁₈ aryl,C₆₋₁₈ aryloxyl, C₇₋₁₈ alkylaryl, or C₇₋₁₈ alkylaryloxyl. In the contextof the neutral aliphatic monomer, “substituted” shall be understood tomean including at least one substituent such as a halogen (i.e., F, Cl,Br, I), carboxyl, ester (including acrylates, methacrylates, andlactones), amide, nitrile, sulfide, disulfide, nitro, C₁₋₁₈ alkyl, C₁₋₁₈alkenyl (including norbornenyl), C₁₋₁₈ alkoxyl, C₂₋₁₈ alkenoxyl(including vinyl ether), C₆₋₁₈ aryl, C₆₋₁₈ aryloxyl, C₇₋₁₈ alkylaryl, orC₇₋₁₈ alkylaryloxyl. “Fluorinated” shall be understood to mean havingone or more fluorine atoms incorporated into the group. For example,where a C₁₋₁₈ fluoroalkyl group is indicated, the fluoroalkyl group caninclude one or more fluorine atoms, for example, a single fluorine atom,two fluorine atoms (e.g., as a 1,1-difluoroethyl group), three fluorineatoms (e.g., as a 2,2,2-trifluoroethyl group), or fluorine atoms at eachfree valence of carbon (e.g., as a perfluorinated group such as —CF₃,—C₂F₅, —C₃F₇, or —C₄F₉).

As used herein, the term “alkyl” includes linear alkyl, branched alkyl,cyclic alkyl, and alkyl groups combining two-way and three-waycombinations of linear, branched, and cyclic groups. The alkyl groupscan be unsubstituted or substituted. Specific examples of alkyl groupsinclude methyl, ethyl, 1-propyl, 2-propyl, cyclopropyl, 1-butyl,2-butyl, 2-methyl-1-propyl, tertiary-butyl, cyclobutyl,1-methylcyclopropyl, 2-methylcyclopropyl, 1-pentyl, 2-pentyl, 3-pentyl,2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl,2,2-dimethyl-1-propyl (neopentyl), cyclopentyl, 1-methylcyclobutyl,2-methylcyclobutyl, 3-methylcyclobutyl, 1,2-dimethylcyclopropyl,2,2-dimethylcyclopropyl, 2,3-dimethylcyclopropyl, 1-hexyl, 2-hexyl,3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl,2-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl,3-methyl-2-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl,3,3-dimethyl-1-butyl, 3,3-dimethyl-2-butyl, 2,3-dimethyl-1-butyl,2,3-dimethyl-2-butyl, 1,2,2-trimethylcyclopropyl,2,2,3-trimethylcyclopropyl, (1,2-dimethylcyclopropyl)methyl,(2,2-dimethylcyclopropyl)methyl, 1,2,3-trimethylcyclopropyl,(2,3-dimethylcyclopropyl)methyl, 2,2-dimethylcyclobutyl,2,3-dimethylcyclobutyl, (1-methylcyclobutyl)methyl,1,2-dimethylcyclobutyl, 2,3-dimethylcyclobutyl,(2-methylcyclobutyl)methyl, 1,3-dimethylcyclobutyl,2,4-dimethylcyclobutyl, (3-methylcyclobutyl)methyl, 1-methylcyclopentyl,2-methylcyclopentyl, cyclopentylmethyl, cyclohexyl, 1-norbornyl,2-norbornyl, 3-norbornyl, 1-adamantyl, 2-adamantyl,octahydro-1-pentalenyl, octahydro-2-pentalenyl, octahydro-3-pentalenyl,octahydro-1-phenyl-1-pentalenyl, octahydro-2-phenyl-2-pentalenyl,octahydro-1-phenyl-3-pentalenyl, octahydro-2-phenyl-3-pentalenyl,decahydro-1-naphthyl, decahydro-2-naphthyl, decahydro-3-naphthyl,decahydro-1-phenyl-1-naphthyl, decahydro-2-phenyl-2-naphthyl,decahydro-1-phenyl-3-naphthyl, and decahydro-2-phenyl-3-naphthyl.

The copolymer comprises repeat units derived from an acid-labilemonomer. In this context, “acid-labile” means that the monomer isreactive with acid derived from photoacid generator. Acid-labilemonomers include carboxylic acid esters, acetals, and ketals.

Illustrative acid-labile carboxylic acid esters include the followingunsubstituted and substituted tertiary hydrocarbyl (meth)acrylates

and combinations thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃.

Illustrative acid-labile acetal- and ketal-substituted monomers include

and combinations thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃.

In some embodiments, the copolymer comprises repeat units derived fromthe acid-labile monomer in an amount of 5 to 40 weight percent,specifically 10 to 35 weight percent, more specifically 10 to 30 weightpercent, based on the total weight of the copolymer.

In addition to repeat units derived from an acid-labile monomer, thecopolymer comprises an aliphatic, lactone-containing monomer.Illustrative examples of aliphatic, lactone-containing monomers include

and combinations thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃.

In some embodiments, the copolymer comprises repeat units derived fromthe aliphatic, lactone-containing monomer in an amount of 10 to 70weight percent, specifically 20 to 60 weight percent, more specifically25 to 50 weight percent, based on the total weight of the copolymer.

The copolymer further comprises repeat units derived from a base-solublemonomer comprising a 1,1,1,3,3,3-hexafluoro-2-hydroxyprop-2-ylsubstituent or a —NH—S(O)₂—R^(b) substituent wherein R^(b) is C₁₋₄perfluoroalkyl. Illustrative examples of such monomers include

and combinations thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃; andR^(b) is C₁₋₄ perfluoroalkyl.

In some embodiments, the copolymer comprises the repeat units derivedfrom the base-soluble monomer in an amount of 3 to 40 weight percent,specifically 5 to 35 weight percent, more specifically 10 to 30 weightpercent, based on the total weight of the copolymer.

The copolymer further comprises repeat units derived from aphotoacid-generating monomer comprising an aliphatic anion. In someembodiments, the photoacid-generating monomer is of the formula

wherein R^(a) is —H, —F, —CH₃, or —CF₃; A is ester-containing ornon-ester-containing, fluorinated or non-fluorinated C₁₋₂₀ alkylene, orC₃₋₂₀ cycloalkylene; Z⁻ is an anionic moiety comprising sulfonate,sulfonamidate (anion of sulfonamide), or sulfonimidate (anion ofsulfonamide); and G⁺ is a sulfonium or iodonium cation.

Illustrative examples of such monomers include

and combinations thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃.

In some embodiments, the copolymer comprises the repeat units derivedfrom the photoacid-generating monomer in an amount of 2 to 30 weightpercent, specifically 2 to 28 weight percent, more specifically 3 to 25weight percent, based on the total weight of the copolymer.

The copolymer further comprises repeat units derived from a neutralaliphatic monomer having the formula

wherein R¹, R², and R³ are each independently hydrogen, halogen, C₁₋₆alkyl, or halogenated C₁₋₆ alkyl; m is 0 or 1; X is —O—, —C(O)—,—C(O)—O—, —S—, —S(O)—, —S(O)₂—, —S(O)₂—N(R⁴)—, —N(R⁴)—S(O)₂—, C₁₋₁₂hydrocarbylene, —O—(C₁₋₁₂ hydrocarbylene)-, —(C₁₋₁₂ hydrocarbylene)-O—,or —C(O)—O—(C₁₋₁₂ hydrocarbylene)-, wherein R⁴ is C₁₋₆ alkyl; and R⁵ isan unsubstituted or substituted C₁₋₂₄ alkyl. In some embodiments, theneutral aliphatic monomer has a calculated Log P (c Log P) value of 2.5to 6. Within this range the c Log P value can be 2.5 to 5. P is thepartition ratio of the monomer between 1-octanol and water. c Log Pvalues can be calculated with, for example, MOLINSPIRATIONCHEMINFORMATICS (http://www.molinspiration.com). The “neutral aliphaticmonomer” can be referred to as the “aliphatic monomer” for brevity. Thestructure of the aliphatic monomer has been defined such that it is freeof groups that become protonated or react in an acidic medium, and freeof groups that become ionized or react in a basic medium. Thus, thecopolymer repeat unit derived from the aliphatic monomer will besubstantially electrically neutral and chemically unreactive in thepresence of photogenerated acid, and in an alkaline developer such as2.38 weight percent tetramethylammonium hydroxide.

In some embodiments of the aliphatic monomer, R¹ and R² are hydrogen; R³is —H, —F, —CH₃, or —CF₃; X is —O—, —C(O)—O—, —(C₁₋₁₂ hydrocarbylene)-,—O—(C₁₋₁₂ hydrocarbylene)-, —(C₁₋₁₂ hydrocarbylene)-O—, or—C(O)—O—(C₁₋₁₂ hydrocarbylene)-; and R⁵ is an unsubstituted orsubstituted C₆₋₁₂ alkyl. In some embodiments, R⁵ is unsubstituted orsubstituted norbornyl, or unsubstituted or substituted adamantyl.

Illustrative examples of neutral aliphatic monomers include

or a combination thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃; eachoccurrence of R^(c) is independently halogen, C₁₋₁₂ hydrocarbyl, C₂₋₁₀alkenyl, C₁₋₆ perfluoroalkyl, or C₃₋₆ perfluorocycloalkyl; R^(e) isC₁₋₁₀ alkylene or C₃₋₁₀ cycloalkylene; R^(f) is C₁₋₁₂ alkyl, C₁₋₆perfluoroalkyl, C₃₋₁₀ cycloalkyl, or C₃₋₆ perfluorocycloalkyl; i is 1,2, 3, or 4; n is 0 or 1; and each occurrence of q is independently 0, 1,2, 3, 4, 5, 6, 7, 8, 9, or 10.

In some embodiments, the copolymer comprises the repeat units derivedfrom the neutral aliphatic monomer in an amount of 1 to 30 weightpercent, specifically 2 to 25 weight percent, more specifically 2 to 20weight percent, based on the total weight of the copolymer.

In some embodiments, the monomers used to form the copolymer comprise nomore than 45 mole percent of monomers comprising an aromatic group.Within this limit, the content of monomers comprising an aromatic groupcan be 5 to 45 mole percent, specifically 5 to 40 mole percent, morespecifically 5 to 35 mole percent.

In some embodiments, the monomers used to prepare the copolymer excludemonomers comprising fluorenyl ester groups. Such monomers are describedin U.S. Pat. No. 8,450,042 B2 to Hatakeyama et al.

In some embodiments, the monomers used to prepare the copolymer excludemonomers having both an acid-labile group that generates a base-solublegroup (e.g., tertiary-alkyl (meth)acrylate ester), and a base-labilegroup that generates a group having increased solubility in alkalideveloper (e.g., a lactone-substituted alkyl (meth)acrylate). Suchmonomers are described in U.S. Patent Application Publication No. US2012/0076997 A1 of Hirano et al. Due to the bulky side chain,polymerization of the monomers is expected to be challenging.

In some embodiments, the copolymer has a weight average molecular weightof 1,000 to 50,000 atomic mass units, specifically 2,000 to 30,000atomic mass units, more specifically 3,000 to 20,000 atomic mass units,still more specifically 3,000 to 10,000 atomic mass units. In someembodiments, the dispersity of the copolymer, which is the ratio ofweight average molecular weight to number average molecular weight is1.1 to 3, specifically 1.1 to 2. Molecular weight values are determinedby gel permeation chromatography using polystyrene standards.

In a very specific embodiment, the acid-labile monomer comprises

the aliphatic, lactone-containing (meth)acrylate ester comprises

the base-soluble monomer comprises

the photoacid-generating monomer comprises

the neutral aliphatic monomer comprises

or a combination thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃; eachoccurrence of R^(c) is independently halogen, C₁₋₁₂ hydrocarbyl, C₂₋₁₀alkenyl, C₁₋₆ perfluoroalkyl, or C₃₋₆ perfluorocycloalkyl; R^(e) isC₁₋₁₀ alkylene or C₃₋₁₀ cycloalkylene; R^(f) is C₁₋₁₂ alkyl, C₁₋₆perfluoroalkyl, C₃₋₁₀ cycloalkyl, or C₃₋₆ perfluorocycloalkyl; i is 1,2, 3, or 4; n is 0 or 1; and each occurrence of q is independently 0, 1,2, 3, 4, 5, 6, 7, 8, 9, or 10.

One embodiment is a photoresist composition comprising the copolymer inany of its above-described variations. The photoresist composition cancontain the copolymer is an amount of 50 to 99.9 weight percent, basedon the total weight of solids (excluding solvent) in the photoresistcomposition. Within this range, the copolymer content of the photoresistcan be 55 to 99.9 weight percent, specifically 65 to 99.9 weightpercent.

The photoresist composition can further include one or more photoactivecomponents such as photoacid generators, photobase generators,photoinitiators, additional (meth)acrylate-based polymers with orwithout bound photoacid generators, hydroxystyrene-based polymers withor without bound photoacid generators, and combinations thereof. Thephotoresist composition can further comprise polymers other than(meth)acrylate-based polymers and hydroxystyrene-based polymers such as,for example, the aromatic polyacetals described in U.S. Nonprovisionalpatent application Ser. No. 13/943,169, filed 16 Jul. 2013.

Photoacid generators can produce an acid when exposed to activatingradiation, such as EUV radiation (e.g., at 193 nanometers), e-beamradiation, and other radiation sources. Photoacid generators generallyinclude those photoacid generators suitable for the purpose of preparingphotoresists. Photoacid generators include, for example, non-ionicoximes and various onium ion salts. Onium ions include, for example,unsubstituted and substituted ammonium ions, unsubstituted andsubstituted phosphonium ions, unsubstituted and substituted arsoniumions, unsubstituted and substituted stibonium ions, unsubstituted andsubstituted bismuthonium ions, unsubstituted and substituted oxoniumions, unsubstituted and substituted sulfonium ions, unsubstituted andsubstituted selenonium ions, unsubstituted and substituted telluroniumions, unsubstituted and substituted fluoronium ions, unsubstituted andsubstituted chloronium ions, unsubstituted and substituted bromoniumions, unsubstituted and substituted iodonium ions, unsubstituted andsubstituted aminodiazonium ions (substituted hydrogen azide),unsubstituted and substituted hydrocyanonium ions (substituted hydrogencyanide), unsubstituted and substituted diazenium ions (RN═N⁺R₂),unsubstituted and substituted iminium ions (R₂C═N⁺R₂), quaternaryammonium ions having two double-bonded substituents (R═N⁺═R), nitroniumion (NO₂ ⁺), bis(trarylphosphine)iminium ions ((Ar₃P)₂N⁺), unsubstitutedor substituted tertiary ammonium having one triple-bonded substituent(R≡NH⁺), unsubstituted and substituted nitrilium ions (RC≡NR⁺),unsubstituted and substituted diazonium ions (N≡N⁺R), tertiary ammoniumions having two partially double-bonded substituents (R

N⁺H

R), unsubstituted and substituted pyridinium ions, quaternary ammoniumions having one triple-bonded substituent and one single-bondedsubstituent (R≡N⁺R), tertiary oxonium ions having one triple-bondedsubstituent (R≡O⁺), nitrosonium ion (N≡O⁺), tertiary oxonium ions havingtwo partially double-bonded substituents (R

O⁺

R), pyrylium ion (C₅H₅O⁺), tertiary sulfonium ions having onetriple-bonded substituent (R≡S⁺), tertiary sulfonium ions having twopartially double-bonded substituents (R

S⁺

R), and thionitrosonium ion (N≡S⁺). In some embodiments, the onium ionis selected from unsubstituted and substituted mono- or diaryliodoniumions, and unsubstituted and substituted mono-, di-, and triarylsulfoniumions. Examples of suitable onium salts can be found in U.S. Pat. No.4,442,197 to Crivello et al., U.S. Pat. No. 4,603,101 to Crivello, andU.S. Pat. No. 4,624,912 to Zweifel et al.

Suitable photo acid generators are known in the art of chemicallyamplified photoresists and include, for example: onium salts, forexample, triphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate; nitrobenzyl derivatives, forexample, 2-nitrobenzyl-p-toluenesulfonate,2,6-dinitrobenzyl-p-toluenesulfonate, and2,4-dinitrobenzyl-p-toluenesulfonate; sulfonic acid esters, for example,1,2,3-tris(methanesulfonyloxy)benzene,1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and1,2,3-tris(p-toluenesulfonyloxy)benzene; diazomethane derivatives, forexample, bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane; glyoxime derivatives, for example,bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime, andbis-O-(n-butanesulfonyl)-α-dimethylglyoxime; sulfonic acid esterderivatives of an N-hydroxyimide compound, for example,N-hydroxysuccinimide methanesulfonic acid ester, N-hydroxysuccinimidetrifluoromethanesulfonic acid ester; and halogen-containing triazinecompounds, for example,2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, and2-(4-methoxynaphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine. Suitablephotoacid generators with specific examples are further described inU.S. Pat. No. 8,431,325 to Hashimoto et al. in column 37, lines 11-47and columns 41-91.

Two specific PAGS are the following PAG 1 and PAG2, the preparation ofwhich is described in U.S. Patent Application Ser. No. 61/701,588, filedSep. 15, 2012.

Other suitable sulfonate PAGS include sulfonated esters and sulfonyloxyketones. See J. of Photopolymer Science and Technology, 4(3):337-340(1991), for disclosure of suitable sulfonate PAGS, including benzointosylate, t-butylphenyl α-(p-toluenesulfonyloxy)-acetate and t-butylα-(p-toluenesulfonyloxy)-acetate. Preferred sulfonate PAGs are alsodisclosed in U.S. Pat. No. 5,344,742 to Sinta et al.

Other useful photoacid generators include the family of nitrobenzylesters, and the s-triazine derivatives. Suitable s-triazine photoacidgenerators are disclosed, for example, in U.S. Pat. No. 4,189,323.

Photoacid generators further include photo-destroyable bases.Photo-destroyable bases include photo-decomposable cations, andpreferably those useful for preparing PAGs, paired with an anion of aweak (pK_(a)>2) acid such as, for example, a C₁₋₂₀ carboxylic acid.Exemplary such carboxylic acids include formic acid, acetic acid,propionic acid, tartaric acid, succinic acid, cyclohexylcarboxylic acid,benzoic acid, salicylic acid, and other such carboxylic acids. Exemplaryphoto-destroyable bases include those combining cations and anions ofthe following structures where the cation is triphenylsulfonium or oneof the following:

where R is independently H, a C₁₋₂₀ alkyl, a C₆₋₂₀ aryl, or a C₆₋₂₀alkyl aryl, and the anion is

where R is independently H, a C₁₋₂₀ alkyl, a C₁₋₂₀ alkoxyl, a C₆₋₂₀aryl, or a C₆₋₂₀ alkyl aryl.

The photoresist can include a photobase generator, including those basedon non-ionic photo-decomposing chromophores such as, for example,2-nitrobenzyl groups and benzoin groups. An exemplary photobasegenerator is ortho-nitrobenzyl carbamate.

The photoresist can include a photoinitiator. Photoinitiators are usedin the photoresist composition for initiating polymerization of thecross-linking agents by generation of free-radicals. Suitable freeradical photoinitiators include, for example, azo compounds, sulfurcontaining compounds, metallic salts and complexes, oximes, amines,polynuclear compounds, organic carbonyl compounds and mixtures thereofas described in U.S. Pat. No. 4,343,885, column 13, line 26 to column17, line 18; and 9,10-anthraquinone; 1-chloroanthraquinone;2-chloroanthraquinone; 2-methylanthraquinone; 2-ethylanthraquinone;2-tert-butylanthraquinone; octamethylanthraquinone; 1,4-naphthoquinone;9,10-phenanthrenequinone; 1,2-benzanthraquinone; 2,3-benzanthraquinone;2-methyl-1,4-naphthoquinone; 2,3-dichloronaphthoquinone;1,4-dimethylanthraquinone; 2,3-dimethylanthraquinone;2-phenylanthraquinone; 2,3-diphenylanthraquinone;3-chloro-2-methylanthraquinone; retenequinone;7,8,9,10-tetrahydronaphthalenequinone; and1,2,3,4-tetrahydrobenz(a)anthracene-7,12-dione. Other photoinitiatorsare described in U.S. Pat. No. 2,760,863 and include vicinal ketaldonylalcohols, such as benzoin, pivaloin, acyloin ethers, e.g., benzoinmethyl and ethyl ethers; and alpha-hydrocarbon-substituted aromaticacyloins, including alpha-methylbenzoin, alpha-allylbenzoin, andalpha-phenylbenzoin. Photoreducible dyes and reducing agents disclosedin U.S. Pat. Nos. 2,850,445; 2,875,047; and 3,097,096 as well as dyes ofthe phenazine, oxazine, and quinone classes; benzophenone,2,4,5-triphenylimidazolyl dimers with hydrogen donors, and mixturesthereof as described in U.S. Pat. Nos. 3,427,161; 3,479,185; and3,549,367 can be also used as photoinitiators.

The photoresist composition can further include a surfactant.Illustrative surfactants include fluorinated and non-fluorinatedsurfactants, and are preferably non-ionic. Exemplary fluorinatednon-ionic surfactants include perfluoro C₄ surfactants such as FC-4430and FC-4432 surfactants, available from 3M Corporation; and fluorodiolssuch as POLYFOX™ PF-636, PF-6320, PF-656, and PF-6520 fluorosurfactantsfrom Omnova.

The photoresist composition can further include quenchers that arenon-photo-destroyable bases. These include, for example, those based onhydroxides, carboxylates, amines, imines and amides. Such quenchersinclude C₁₋₃₀ organic amines, imines or amides, C₁₋₃₀ quaternaryammonium salts of strong bases (e.g., a hydroxide or alkoxide) or a weakbase (e.g., a carboxylate). Exemplary quenchers include amines such astripropylamine, dodecylamine, tris(2-hydroxypropyl)amine,tetrakis(2-hydroxypropyl)ethylenediamine; aryl amines such asdiphenylamine, triphenylamine, aminophenol, and2-(4-aminophenyl)-2-(4-hydroxyphenyl)propane, Troger's base; hinderedamines such as diazabicycloundecene (DBU), diazabicyclononene (DBN), andtetrahydroxy isopropyl diamine and tert-butyl-4-hydroxy-1-piperidienecarboxylate; ionic quenchers including quaternary alkyl ammonium saltssuch as tetrabutylammonium hydroxide (TBAH), tetramethylammonium2-hydroxybenzoic acid (TMA OHBA), and tetrabutylammonium lactate.Suitable quenchers are further described in U.S. Pat. No. 8,431,325 toHashimoto et al.

The photoresist components are typically dissolved in a solvent fordispensing and coating. Exemplary solvents include anisole; alcoholsincluding 1-methoxy-2-propanol, and 1-ethoxy-2 propanol; estersincluding n-butyl acetate, ethyl lactate, 1-methoxy-2-propyl acetate,methoxyethoxy propionate, ethoxyethoxy propionate, and methyl2-hydroxyisobutyrate; ketones including cyclohexanone and 2-heptanone;and combinations thereof. The solvent amount can be, for example, 70 to99 weight percent, specifically 85 to 98 weight percent, based on thetotal weight of the photoresist composition.

Photoresist compositions also may contain other materials. For example,other optional additives include actinic and contrast dyes,anti-striation agents, plasticizers, speed enhancers and sensitizers.Such optional additives typically will be present in minor concentrationin a photoresist composition.

In some embodiments, the photoresist composition in solution comprisesthe polymer in an amount of 50 to 99.9 weight percent, specifically 55to 99.9 weight percent, more specifically 65 to 99.9 weight percent,based on the total weight of solids. It will be understood that“polymer” used in this context of a component in a photoresist may meanonly the copolymer disclosed herein, or a combination of the copolymerwith another polymer useful in a photoresist. The photo-destroyable basemay be present in the photoresist in an amount of 0.01 to 5 weightpercent, specifically 0.1 to 4 weight percent, more specifically 0.2 to3 weight percent, based on the total weight of solids. A surfactant maybe included in an amount of 0.01 to 5 weight percent, specifically 0.1to 4 weight percent, more specifically 0.2 to 3 weight percent, based onthe total weight of solids. A photoacid generator is included in theamounts of 0 to 50 weight percent, specifically 1.5 to 45 weightpercent, more specifically 2 to 40 weight percent, based on the totalweight of solids. A quencher may be included in relatively small amountsof for example, from 0.03 to 5 weight percent based on the total weightof solids. Other additives may be included in amounts of less than orequal to 50 weight percent, specifically less than or equal to 35 weightpercent, or more specifically less than or equal to 25 weight percent,based on the total weight of solids. The total solids content for thephotoresist composition may be 0.5 to 50 weight percent, specifically 1to 45 weight percent, more specifically 2 to 40 weight percent, andstill more specifically 5 to 30 weight percent. It will be understoodthat total solids includes polymer, photo-destroyable base, quencher,surfactant, any added PAG, and any optional additives, exclusive ofsolvent.

Another embodiment is a negative tone photoresist comprising thecopolymer. Preferred negative-acting compositions comprise a mixture ofmaterials that will cure, crosslink, or harden upon exposure to acid,and one, two, or more photoacid generators as disclosed herein.Preferred negative acting compositions comprise a polymer binder such asa phenolic or non-aromatic polymer, a crosslinker component and aphotoactive component of the invention. Such compositions and the usethereof have been disclosed in European Patent Application No. EP0164248A2 of Feely, and U.S. Pat. No. 5,128,232 to Thackeray et al. Preferredphenolic polymers for use as the polymer binder component includenovolaks and poly(vinylphenol)s. Preferred crosslinkers includeamine-based materials, including melamine, glycolurils,benzoguanamine-based materials, and urea-based materials.Melamine-formaldehyde polymers are often particularly suitable. Suchcrosslinkers are commercially available, e.g. the melamine polymers,glycoluril polymers, urea-based polymer and benzoguanamine polymers,such as those sold by Cytec under tradenames CYMEL™ 301, 303, 1170,1171, 1172, 1123 and 1125 and BEETLE™ 60, 65 and 80.

Another embodiment is a coated substrate comprising: (a) a substratehaving one or more layers to be patterned on a surface thereof; and (b)a layer of the photoresist composition over the one or more layers to bepatterned.

The substrate can be of a material such as a semiconductor, such assilicon or a compound semiconductor (e.g., III-V or II-VI), glass,quartz, ceramic, copper and the like. Typically, the substrate is asemiconductor wafer, such as single crystal silicon or compoundsemiconductor wafer, having one or more layers and patterned featuresformed on a surface thereof. Optionally, the underlying base substratematerial itself may be patterned, for example, when it is desired toform trenches in the base substrate material. Layers formed over thebase substrate material may include, for example, one or more conductivelayers such as layers of aluminum, copper, molybdenum, tantalum,titanium, tungsten, and alloys, nitrides or silicides of such metals,doped amorphous silicon or doped polysilicon, one or more dielectriclayers such as layers of silicon oxide, silicon nitride, siliconoxynitride or metal oxides, semiconductor layers, such as single-crystalsilicon, underlayers, antireflective layers such as a bottomantireflective layers, and combinations thereof. The layers can beformed by various techniques, for example, chemical vapor deposition(CVD) such as plasma-enhanced CVD, low-pressure CVD or epitaxial growth,physical vapor deposition (PVD) such as sputtering or evaporation,electroplating or spin-coating.

The invention further includes a method of forming an electronic device,comprising: (a) applying a layer of any of the photoresist compositionsdescribed herein on a substrate; (b) pattern-wise exposing thephotoresist composition layer to activating (e.g., ultraviolet orelectron beam) radiation; (c) developing the exposed photoresistcomposition layer to provide a resist relief image. The method can,optionally, further include (d) etching the resist relief pattern intothe underlying substrate.

Applying the photoresist composition to the substrate can beaccomplished by any suitable method, including spin coating, spraycoating, dip coating, and doctor blading. In some embodiments, applyingthe layer of photoresist composition is accomplished by spin coating thephotoresist in solvent using a coating track, in which the photoresistcomposition is dispensed on a spinning wafer. During dispensing, thewafer can be spun at a speed of up to 4,000 rotations per minute (rpm),specifically 500 to 3,000 rpm, and more specifically 1,000 to 2,500 rpm.The coated wafer is spun to remove solvent, and baked on a hot plate toremove residual solvent and free volume from the film to make ituniformly dense.

Pattern-wise exposure is then carried out using an exposure tool such asa stepper, in which the film is irradiated through a pattern mask andthereby is exposed pattern-wise. In some embodiments, the method usesadvanced exposure tools generating activating radiation at wavelengthscapable of high resolution including extreme-ultraviolet (EUV) orelectron-beam (e-beam) radiation. It will be appreciated that exposureusing the activating radiation decomposes the PAG in the exposed areasand generates acid and decomposition by-products, and that the acid theneffects a chemical change in the polymer (deblocking the acid sensitivegroups to generate a base-soluble group, or alternatively, catalyzing across-linking reaction in the exposed areas) during the post exposurebake (PEB) step. The resolution of such exposure tools can be less than30 nanometers.

Developing the exposed photoresist layer is then accomplished bytreating the exposed layer with a suitable developer capable ofselectively removing the exposed portions of the film (where thephotoresist is positive tone) or removing the unexposed portions of thefilm (where the photoresist is crosslinkable in the exposed regions,i.e., negative tone). In some embodiments, the photoresist is positivetone based on a polymer having acid-sensitive (deprotectable) groups,and the developer is preferably a metal-ion-free tetraalkylammoniumhydroxide solution, such as, for example, aqueous 0.26 Normaltetramethylammonium hydroxide. Alternatively, negative tone development(NTD) can be conducted by use of a suitable organic solvent developer.NTD results in the removal of unexposed regions of the photoresistlayer, leaving behind exposed regions due to polarity reversal of thoseregions. Suitable NTD developers include, for example, ketones, esters,ethers, hydrocarbons, and mixtures thereof. Other suitable solventsinclude those used in the photoresist composition. In some embodiments,the developer is 2-heptanone or a butyl acetate such as n-butyl acetate.Whether the development is positive tone or negative tone, a patternforms by developing.

The photoresist can, when used in one or more such a pattern-formingprocesses, be used to fabricate electronic and optoelectronic devicessuch as memory devices, processor chips (including central processingunits or CPUs), graphics chips, and other such devices.

The invention is further illustrated by the following examples.

EXAMPLES

The acronyms and chemical structures of monomers used in these examplesare presented in Table 1.

TABLE 1 Monomer Acronym Monomer Structure α-GBLMA

CF3PPMA

DiHFA

ECP PDBT- F2

PDBT-F2

PPMA

TBPPDBT- F2

ADMA

Synthesis of a (Comparative) PPMA/α-GBLMA/DiHFA/TBPPDBT-F2 Copolymer.

A feed solution was made by dissolving PPMA (41.2 grams), α-GBLMA (45.35grams), DiHFA (28.48 grams) and TBP PDBTS-F₂ (13.96 grams) in 130.8grams of a 30:70 (v/v) mixture of ethyl lactate and gamma-butyrolactone.A heel solution was prepared by dissolving PPMA (2.69 grams), α-GBLMA(2.24 grams), DiHFA (3.92 grams) and TBPPDBTS-F₂ (2.13 grams) in 86.5grams of a 30:70 (v/v) mixture of ethyl lactate and gamma-butyrolactone.An initiator solution was prepared by dissolving 14.6 grams of the azoinitiator 2,2′-azobis(2,4-dimethyl valeronitrile) (obtained as V-65 fromWako Pure Chemical Industries, Ltd.) in 14.6 grams of a 2:1 (v/v)mixture of acetonitrile and tetrahydrofuran (THF).

The polymerization was carried out in a 2-liter, 3-neck round bottomflask fitted with a water condenser and a thermometer to monitor thereaction in the flask. The contents were stirred using an overheadstirrer. The reactor was charged with the heel solution and the contentswere heated to 75° C. The feed solution and the initiator solution werefed into the reactor using syringe pumps over a 4 hour time period. Thecontents were then stirred for additional 2 hours, after which thereaction was quenched using hydroquinone (2.0 grams). The contents werecooled to room temperature, diluted with THF to 25 weight percent, andprecipitated twice out of 10-fold (by weight) of a 95:5 (w/w) mixture ofdiisopropyl ether (IPE) and methanol (MeOH). After each precipitationstep, the polymer obtained was dried under vacuum at 50° C. for 24 hoursto yield 99 grams of a PPMA/α-GBLMA/DiHFA/TBPPDBT-F2 copolymer havingthe respective repeat units in a 34:50:10:6 mole ratio and a weightaverage molecular weight of 5,300 atomic mass units. This copolymer isdesignated Copolymer 1.

Synthesis of a (Comparative) CF3PPMA/α-GBLMA/DiHFA/PDBT-F2 Copolymer.

A similar procedure was used to prepare a CF3PPMA/α-GBLMA/DiHFA/PDBT-F2copolymer having the respective repeat units in a 36:47:11:6 mole ratioand a weight average molecular weight of 5,000 atomic mass units. Thiscopolymer is designated Copolymer 2.

Lithographic Evaluation of PPMA/α-GBLMA/DiHFA/TBPPDBT-F2 andCF3PPMA/α-GBLMA/DiHFA/PPDBT-F2 Copolymers.

Table 2 summarizes the compositions and processing conditions forphotoresists incorporating the PPMA/α-GBLMA/DiHFA/TBPPDBT-F2 andCF3PPMA/α-GBLMA/DiHFA/PDBT-F2 copolymers. In table two, componentamounts are expressed in weight percent based on total solids excludingsolvents. In Table 2, the photoacid generator DiMADMeOAC PDBT-ADOH hasthe chemical structure

Also in Table 2, “PDQ” is photodecomposable quencher. The PDQTBPPDBT-ADCA has the chemical structure

The quencher THIPDA has the chemical structure

The surfactant POLYFOX™ PF-656, obtained from OMNOVA SOLUTIONS INC., hasthe chemical structure

where x+y is, on average, about 6. “EL” is ethyl lactate, “HBM” ismethyl 2-hydroxybutyrate.

TABLE 2 Comparative Example 1 Comparative Example 2 Copolymer 75.02%Copolymer 1 99.75% Copolymer 2 PAG 23.67% DiMADMeOAC none PDBT-ADOH PDQ,1.0016% TBPPDBT- 0.149% THIPDA Quencher ADCA, 0.225% THIPDA Surfactant0.075% POLYFOX ™ 0.0998% POLYFOX ™ solution PF-656 in 70:30 PF-656 in70:30 (w/w) EL/HBM (w/w) EL/HBM Soft bake 110° C. for 90 seconds 130° C.for 90 seconds conditions Post-exposure 100° C. for 60 seconds 100° C.for 60 seconds bake conditions

FIG. 1 shows contact hole and line/space performance for the ComparativeExample 1 photoresist, which was optimized for contact hole exposures,and the Comparative Example 2 photoresist, which was optimized for lineexposures. For Comparative Example 1, 30 nanometer contact holes werewell printed at 51 millijoules/centimeter² with a critical dimensionuniformity (CDU) of 2.82 nanometers (FIG. 1( a)). However, when the sameresist was evaluated for line/space application, resolution was limitedby pattern collapse at 22 nanometers half pitch (FIG. 1( b)). ForComparative Example 2, a 17 nanometer resolution line/space was obtained(FIG. 1( c)), but the contact hole performance (FIG. 1( d)) wassignificantly worse than that of Comparative Example 1.

To address the question of why a contact hold resist fails in aline/space exposure and a line/space resist fails in a contact holeexposure, the above photoresist compositions were analyzed by monitoringthe dissolution rate (DR) in tetramethylammonium hydroxide developer(0.26 Normal tetramethylammonium hydroxide, a standard developer used inthe positive tone development) under 248 nanometer exposure. Thedissolution rate data plotted in FIG. 2 were generated using adissolution rate monitoring tool, LTJ ARM 800, employing a 470 nanometermonitoring wavelength. In the FIG. 2 plot, the x-axis is exposure dose,expressed in units of millijoules/centimeter² and plotted on a logscale, and the y-axis is dissolution rate, expressed in units ofnanometers/second and plotted on a log scale. The Comparative Example 1photoresist exhibits a higher R_(max) value (about 7586nanometers/second) and a steep contrast (Tan θ). In contrast, theComparative Example 2 photoresist was characterized by a much shallowerdissolution contrast and lower R_(max) and R_(min). The difference inperformance of these resists is consistent with the difference indissolution rates.

Since dissolution rate would be dependent on acid labile group contentin the copolymer, three PPMA/α-GBLMA/DiHFA/PDBT-F2 copolymers withdifferent levels of acid-labile monomers were synthesized and aresummarized in Table 3. The 36/45/11/5 copolymer is the control systemwith 36 mole percent acid-labile monomer. The other two copolymers weresynthesized with 26 and 21 mole percent acid-labile monomer. Eachcopolymer had a weight average molecular weight of about 5,000 atomicmass units.

TABLE 3 Copolymer Monomers Monomer Ratio 3 PPMA/α-GBLMA/DiHFA/PDBT-F236:48:11:5 4 PPMA/α-GBLMA/DiHFA/PDBT-F2 26:57:11:6 5PPMA/α-GBLMA/DiHFA/PDBT-F2 21:63:8:8

Photoresist compositions containing Copolymers 3-5 were formulated assummarized in Table 4, where component amounts are based on totalsolids, excluding solvents.

TABLE 4 Photoresist C. Ex. 3 C. Ex. 4 C. Ex. 5 Copolymer 99.75% Copolym.99.75% Copolym. 99.75% Copolym. 3 4 5 Quencher 0.15% THIPDA 0.15% THIPDA0.15% THIPDA Surfactant 0.0998% 0.0998% 0.0998% solution POLYFOX ™POLYFOX ™ POLYFOX ™ PF-656 in 70:30 PF-656 in 70:30 PF-656 in 70:30(w/w) EL/HBM (w/w) EL/HBM (w/w) EL/HBM Soft-bake 110° C. for 90 110° C.for 90 110° C. for 90 conditions seconds seconds seconds Post-exposure100° C. for 60 100° C. for 60 100° C. for 60 bake seconds secondsseconds conditions

Photolithographic results are presented in Table 5, where “UFTL” is theunexposed film thickness loss, expressed in Angstroms, “R_(min),” is thedissolution rate of unexposed resist expressed in nanometers per second,“R_(max)” is the dissolution rate of fully exposed resist expressed innanometers per second, and “248 nm E₀” is the 248 nanometer exposuredose to clear expressed in millijoules/centimeter². The results showthat the copolymers with lower acid-labile monomer contents exhibitedsignificant reductions in R_(max). Since the UFTL values for ComparativeExamples 4 and 5 were significantly elevated, they were not evaluated byEUV lithography. A high UFTL could potentially impart severe top loss(mottling) and reduce the aspect ratio after the development cycle.

TABLE 5 UFTL R_(min) R_(max) 248 nm E₀ Photoresist (Å) (nm/s) (nm/s)(mJ/cm²) C. Ex. 3 8 0.005 6930 27 C. Ex. 4 29 0.03 3376 24 C. Ex. 5 540.04 1935 24

Additional copolymers were synthesized to explore the effects ofincorporating the neutral aliphatic monomer, ADMA. The copolymercompositions are summarized in Table 6. Copolymer 8 was synthesized asfollows. A heel solution was made by dissolving PPMA (0.44 grams),α-GBLMA (0.36 grams), DiHFA (0.63 grams) and TBPPDBT-F2 (0.34 grams) in16.35 grams of a 70:30 (v/v) mixture of gamma-butyrolactone and ethyllactate. A feed solution was prepared by dissolving PPMA (4.78 grams),α-GBLMA (7.25 grams), DiHFA (4.78 grams), ADMA (2.07 grams) andTBPPDBT-F2 (2.57 grams) in 21.16 grams of a 70:30 (v/v) mixture ofgamma-butyrolactone and ethyl lactate. An initiator solution wasprepared by dissolving 2.34 gram of the azo initiator2,2′-azobis(2,4-dimethyl valeronitrile) (obtained from Wako PureChemical Industries, Ltd.) in 2.34 grams of 2:1 (v/v) mixture ofacetonitrile and tetrahydrofuran. The polymerization was carried out ina 300 milliliter, three-neck round-bottom flask fitted with a watercondenser and a thermometer to monitor the reaction temperature in theflask. The reactor was charged with the heel solution and the contentswere heated to 75° C. The feed solution and initiator solution were fedinto the reactor using syringe pumps over a period of 4 hours. Thecontents were then stirred for an additional 2 hours, after which thereaction was quenched using hydroquinone (0.2 grams). The contents werecooled to room temperature, diluted with THF to 25 weight percent, andprecipitated twice out of 10-fold (by weight) of a 95:5 (w/w) mixture ofdiisopropyl ether and methanol. The polymer obtained after eachprecipitation step was dried under vacuum at 50° C. for 24 hours toyield 8 grams of PPMA/α-GBLMA/DiHFA/ADMA/TBPPDBT-F2 copolymer (Copolymer6). Other polymers listed in Table 6 were synthesized in a similar wayexcept for a change in the type and/or content of the neutral monomeremployed.

TABLE 6 Copolymer Monomers Monomer Ratio 6 PPMA/α-GBLMA/DiHFA/TBPPDBT-F235/48/12/5 7 PPMA/α-GBLMA/DiHFA/TBPPDBT-F2 26/58/11/5 8PPMA/α-GBLMA/DiHFA/TBPPDBT-F2/ 26/47/12/5/10 ADMA 9PPMA/α-GBLMA/DiHFA/TBPPDBT-F2/ 16/47/12/5/20 ADMA 10PPMA/α-GBLMA/DiHFA/ECPPDBT-F2 36/47/12/5

Photoresist compositions containing Copolymers 6-10 were formulated assummarized in Table 7, where component amounts are based on totalsolids, excluding solvents. The photoacid generator TBPPDBT DHC has thechemical structure

All formulations in Table 7 used a 70:30 (w/w) mixture of ethyl lactateand gamma-butyrolactone as solvent. The resists were processed at a softbake of 110° C. for 90 seconds and a post-exposure base at 100° C. for60 seconds. Contrast curves at 248 nanometers were generated by coatingthe resist on a 60 nanometer thick organic antireflective layer (DowElectronic Materials AR™ 9-900). The resist was exposed at 248nanometers on a Canon TELACT tool. After post-exposure bake, the resistswere developed for 60 seconds using 0.26 Normal tetramethylammoniumhydroxide solution. Film thickness values were measured using KLATencore OPTIPROBE™ 7341 thermal wave tool.

TABLE 7 Photoresist Copolymer Quencher PAG surfactant C. Ex. 6 99.75%0.149% none 0.099% Copolymer 6 THIPDA POLYFOX ™ PF-656 C. Ex. 7 99.75%0.149% none 0.099% Copolymer 7 THIPDA POLYFOX ™ PF-656 Ex. 1 99.75%0.149% none 0.099% Copolymer 8 THIPDA POLYFOX ™ PF-656 Ex. 2 72.56%0.82% 26.5% 0.072% Copolymer 8 THIPDA TBPPDBT POLYFOX ™ DHC PF-656 Ex. 399.75% 0.149% none 0.099% Copolymer 9 THIPDA POLYFOX ™ PF-656 Ex. 472.56% 0.82% 26.5% 0.072% Copolymer 9 THIPDA TBPPDBT POLYFOX ™ DHCPF-656 C. Ex. 8 72.37% 1.085% 26.4% 0.072% Copolymer 12 TIPA TBPPDBTPOLYFOX ™ DHC PF-656 *TIPA = triisopropylamine

Photolithographic results are summarized in Table 8 for the photoresistcompositions of Table 7. In Table 8, “EUV Es” is the sizing energy,expressed in millijoules/centimeter², at 26 nanometer critical dimensionusing extreme ultraviolet exposure. For the photoresist compositionswith no added PAG (Comparative Examples 6 and 7, and Examples 1 and 3),the inventive photoresists of Examples 1 and 3 incorporated a copolymerwith repeat units derived from a neutral aliphatic monomer, exhibitedlower R_(max) values relative to Comparative Example 6, in which thecopolymer that does not incorporate a neutral aliphatic monomer, andComparative Examples 7, in which the copolymer that does not incorporatea neutral aliphatic monomer and does have a lower content of acid-labilegroups. It was also observed that the incorporation of the neutralaliphatic monomer in the Copolymers of Examples 1 and 3, even with loweracid labile group content, yields a UFTL which was significantly lowerthan that of the photoresist in Comparative Example 7. This result isunlike the one shown in Table 5, where the decrease in the acid labilegroup content in the copolymer was associated with a significantincrease in UFTL. For the photoresist compositions of ComparativeExample 8 and Examples 2 and 4, which contain added PAG in theformulation, the inventive photoresists of Examples 2 and 4, in whichthe copolymer incorporates a neutral aliphatic monomer, exhibited muchlower R_(max) values relative to Comparative Example 8. A higher UFTLand R_(min) were observed for all formulations containing added PAG asopposed to low UFTL and R_(min) for compositions without added PAG.

TABLE 8 EUV Es 248 nm E₀ 26 nm CD UFTL R_(min) R_(max) Photoresist(mJ/cm²) (mJ/cm²) (Å) (nm/s) (nm/s) Tanθ C. Ex. 6 38 15.29 4 0.005 450012 C. Ex. 7 45 15.29 16 0.01 2400 12 Ex. 1 61 24.3 1 0.005 1697 12 Ex. 243 21.2 14 0.01 1831 15 Ex. 3 103 — 3 0.004 166 11 Ex. 4 75 45.5 150.017 1341 10 C. Ex. 8 36 14.0 13 0.009 7374 18

The Example 3 photoresist was not evaluated for EUV lithography due toslow photo speed. The Example 2 and Comparative Example 8 photoresistswere evaluated for line/space performance at the Albany eMET tool. Thephotoresists were coated at a 40 nanometer thickness on a silicon waferthat had been pre-coated at a 25 nanometer thickness with apolyester-based antireflective layer. The Examples 1 and 4 andComparative Examples 6 and 7 photoresists were evaluated at the LawrenceBerkeley National Laboratory (LBNL) eMET tool. The photoresists werecoated at 35 nanometer thickness (Example 1) or 50 nanometer thickness(Example 4 and Comparative Examples 6 and 7) on an antireflective layer.The resist was pre-baked at 110° C. for 90 seconds followed by apattern-wise exposure with EUV light. After post-exposure bake at 100°C. for 60 seconds, the resist was developed with 0.26 Normaltetramethylammonium hydroxide for 30 seconds. FIG. 3 shows the 26nanometer line/space performance for the inventive photoresist ofExample 1 and 3, and comparative photoresists of Comparative Examples 3,6, and 7. The top-down scanning electron micrographs of the inventivephotoresists of Examples 1 and 3 exhibit a reduction in mottling atoverexposure (21 nanometer critical dimension).

FIG. 4 shows the 26 nanometer line space performance for the inventivephotoresist of Example 2 and the comparative photoresist of ComparativeExample 8. The inventive photoresists of Example 2 exhibits a reductionin mottling and increase in depth of focus.

FIG. 5 shows the 22 nanometer line/space performance for Example 2 andComparative Example 8. The inventive photoresists of Example 2 exhibitsa reduction in mottling and increase in depth of focus.

1. A copolymer comprising repeat units derived from an acid-labilemonomer; an aliphatic, lactone-containing monomer; a base-solublemonomer comprising a 1,1,1,3,3,3-hexafluoro-2-hydroxyprop-2-ylsubstituent or a —NH—S(O)₂—R^(b) substituent wherein R^(b) is C₁₋₄perfluoroalkyl; a photoacid-generating monomer comprising an aliphaticanion; and a neutral aliphatic monomer having the formula

wherein R¹, R², and R³ are each independently hydrogen, halogen, C₁₋₆alkyl, or halogenated C₁₋₆ alkyl; m is 0 or 1; X is —O—, —C(O)—,—C(O)—O—, —S—, S(O)—, —S(O)₂—, —S(O)₂—N(R⁴)—, —N(R⁴)—S(O)₂—, C₁₋₁₂hydrocarbylene, —O—(C₁₋₁₂ hydrocarbylene)-, —(C₁₋₁₂ hydrocarbylene)-O—,or —C(O)—O—(C₁₋₁₂ hydrocarbylene)-, wherein R⁴ is C₁₋₆ alkyl; and R⁵ isan unsubstituted or substituted C₁₋₂₄ alkyl.
 2. The copolymer of claim1, wherein the neutral aliphatic monomer has a c Log P of 2.5 to
 6. 3.The copolymer of claim 1, wherein the acid-labile monomer comprises anunsubstituted or substituted tertiary hydrocarbyl (meth)acrylatecomprising

or a combination thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃.
 4. Thecopolymer of claim 1, wherein the base-soluble monomer comprises

or a combination thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃; andR^(b) is C₁₋₄ perfluoroalkyl.
 5. The copolymer of claim 1, wherein thephotoacid-generating monomer comprises

or a combination thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃.
 6. Thecopolymer of claim 1, wherein R¹ and R² are hydrogen; R³ is —H, —F,—CH₃, or —CF₃; X is —O—, —C(O)—O—, —(C₁₋₁₂ hydrocarbylene)-, —O—(C₁₋₁₂hydrocarbylene)-, —(C₁₋₁₂ hydrocarbylene)-O—, or —C(O)—O—(C₁₋₁₂hydrocarbylene)-; and R⁵ is an unsubstituted or substituted C₆₋₁₂ alkyl.7. The copolymer of claim 1, wherein the neutral aliphatic monomercomprises

or a combination thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃; eachoccurrence of R^(c) is independently halogen, C₁₋₁₂ hydrocarbyl, C₂₋₁₀alkenyl, C₁₋₆ perfluoroalkyl, or C₃₋₆ perfluorocycloalkyl; R^(e) isC₁₋₁₀ alkylene or C₃₋₁₀ cycloalkylene; R^(f) is C₁₋₁₂ alkyl, C₁₋₆perfluoroalkyl, C₃₋₁₀ cycloalkyl, or C₃₋₆ perfluorocycloalkyl; i is 1,2, 3, or 4; n is 0 or 1; and each occurrence of q is independently 0, 1,2, 3, 4, 5, 6, 7, 8, 9, or
 10. 8. The copolymer of claim 1, wherein theacid-labile monomer comprises

wherein the aliphatic, lactone-containing (meth)acrylate ester comprises

wherein the base-soluble monomer comprises

wherein the photoacid-generating monomer comprises

and wherein the neutral aliphatic monomer comprises

or a combination thereof, wherein R^(a) is —H, —F, —CH₃, or —CF₃; eachoccurrence of R^(c) is independently halogen, C₁₋₁₂ hydrocarbyl, C₂₋₁₀alkenyl, C₁₋₆ perfluoroalkyl, or C₃₋₆ perfluorocycloalkyl; R^(e) isC₁₋₁₀ alkylene or C₃₋₁₀ cycloalkylene; R^(f) is C₁₋₁₂ alkyl, C₁₋₆perfluoroalkyl, C₃₋₁₀ cycloalkyl, or C₃₋₆ perfluorocycloalkyl; i is 1,2, 3, or 4; n is 0 or 1; and each occurrence of q is independently 0, 1,2, 3, 4, 5, 6, 7, 8, 9, or
 10. 9. A photoresist composition comprisingthe copolymer of claim
 1. 10. A coated substrate comprising: (a) asubstrate having one or more layers to be patterned on a surfacethereof; and (b) a layer of the photoresist composition of claim 9 overthe one or more layers to be patterned.
 11. A method of forming anelectronic device, comprising: (a) applying a layer of a photoresistcomposition of claim 9 on a substrate; (b) pattern-wise exposing thephotoresist composition layer to activating radiation; and (c)developing the exposed photoresist composition layer to provide a resistrelief image.